By Patrick Lee, MD, PGY-2

Dr. Katushiro Kobayashi is currently an Associate Professor of Radiology at the State University of New York Upstate Medical University. He completed his Diagnostic Radiology residency at the Shiga University of Medical Science in Japan and subsequently practiced for a number of years as a diagnostic and interventional radiologist in Kyoto, Japan. He then completed a Vascular and Interventional Radiology Fellowship at the University of Texas at Houston. His dual training gives him an interesting perspective into the differences between the different IR practices in the United States and Japan.

Can you describe your journey to becoming an IR? Were you always interested in Radiology? What made you wish to become an IR?

When I was a medical student in Japan, I had a chance to observe a chemoembolization procedure for hepatocellular carcinoma during my clinical rotation in Radiology. The way the patient was treated did intrigue me. The patient only had a small hole at the groin through which a small tube was put into an artery. The tube reached the tumor, oily material (lipiodol) mixed with chemo agents were put through the tube and nicely accumulated in the tumor. I thought that it was a smart way to treat cancer patients and this specialty looked very promising to me. This is one of the reasons why I got into IR.

Can you explain the training pathway to become an IR in Japan? Is there a dedicated residency or postgraduate training pathway? Recently, in the United States, a new independent IR/DR residency was launched. What are your thoughts on something similar for Japan?

After becoming a board-certified radiologist, two years of IR training at a certified training institution are required to sit for an IR board examination. There is no dedicated IR residency or IR/DR residency over there, however I believe that it is ideal for residents who wish to become an interventional radiologist to go through an independent IR training pathway. However, it would not be realistic to have such a pathway in Japan given the limited number of interventional radiologists and diagnostic radiologists. The number of radiologists are approximately one third of that of the US. Notably, the number of CT and MR examinations per a radiologist is almost three times more in Japan than that in the US (1). For this reason, even after being a board-certified interventional radiologist, it is not uncommon to read diagnostic studies while working as an interventional radiologist.

While still uncommon in the US, are independent IR departments common in Japan? Is IR a separate department from the Diagnostic Radiology Department at most hospitals? What are your thoughts on this split?

Independent IR departments are quite uncommon even in major academic centers in Japan. Regardless of the country you work in, I personally feel that IR should seek independence from Radiology, allowing us to have more autonomy and a better infrastructure for future development of IR.

In the US, there has been a push for IRs to take care of patients clinically. Is there a clinical model for IR in Japan?

In some major academic centers, IRs have their own ward where they admit the patients following IR procedures. Also, they follow the patients in their outpatient clinic. However, this pattern of practice is uncommon due to the limited number of interventional radiologists.

Having practiced in both the US and Japan, are there any crucial differences you see? Are there turf wars in Japan like there are in the US?

As noted previously, the biggest difference in an interventional radiology practice (and diagnostic radiology in general) between the two countries is manpower.  Physician assistants or nurse practitioners whom IR physicians can delegate part of their jobs are few in Japan. Also, it is not uncommon for interventional radiologists to have a heavy diagnostic radiology duty in their practice.

Another difference I see is that the Japanese government is much more conservative in approving new devices which are being used already in other countries. For instance, yttrium-90 radioembolization has not been approved in Japan yet. These differences may be related to the difference in the medical insurance system.

Speaking of turf battles, they appear to be more severe in Japan, partly because of limited IR manpower. For instance, urologic interventions such as nephrostomies are mostly being done by urologists. I believe that IR physicians in the US have wider coverage of IR procedures and this is one of the reasons why I sought IR training in the US.

Are there any novel procedures being performed in Japan that you are aware of?

Some procedures which have been performed in Japan for a long time are becoming popular in US. For instance, balloon-occluded retrograde transvenous obliteration (BRTO) of gastric varices is becoming a common procedure in the US, however, it was already quite popular in Japan 20 years ago. Also, percutaneous transesophageal gastrotubing (PTEG) which involves percutaneous insertion of a tube through the cervical esophagus for patients with obstructing gastric cancer or carcinomatous peritonitis, has been performed in Japan for over a decade now, although it is not well known in the US (2).


  • Global and Japanese regional vairations in radiologist potential workload for computed tomography and magnetic resonance imaging examinations. Kumamaru KK, Machitori A, Koba R, Ijichi S, Nakajima Y, Aoki S. Japanese Journal of Radiology (2018) 36:273-281
  • Phase II study of percutaneous transesophageal gastrotubing for patients with malignant gastrointestinal obstruction; JIVROSG-0205. Aramaki T1Arai YInaba YSato YSaito HSone MTakeuchi Y. J Vasc Interv Radiol.2013 Jul;24(7):1011-7.